string printing reference in java

Question

I have this code where I am printing a string variable. The first output is showing what is expected but the second time it prints some unreadable output(I think its reference id). Please explain: Why does this happen?

public class Str3 {
    public String frontBack(String str) {
        char c[] = str.toCharArray();
        char temp = c[0];
        c[0] = c[c.length - 1];
        c[c.length - 1] = temp;
        return c.toString();
    }

    public static void main(String args[]) {
        Str3 s = new Str3();
        String s1 = new String("boy");
        System.out.println(s1);
        String s2 = s.frontBack("boy");
        System.out.println(s2);
    }
}

Output:

boy

[C@60aeb0

Answer 1

the frontToBack() method is calling toString() on a character array object char[] which is why you see the [C@60aebo . Instead of calling toString() return with new String(c); or String.valueOf(c)

Answer 2

Array types in Java do not override Object#toString() . In other words, array types inherit Object 's implementation of toString() which is just

public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

which is the output you see

[C@60aeb0

If you want to see a representation of the contents of an array, use Arrays.toString(..) .

In your case, you seem to want to switch the first and last characters and return the corresponding string. In that case, just create a new String instance by passing the char[] to the constructor.

Answer 3

You don't need to implement a custom class to do this. The functionality is already in java. This question has already been answered @ Reverse a string in Java (duplicate thread)

Answer 4

use new String(c) to c.toString();

c.toString() c mean array of chars toString() print hash method

public class Str3 {

public String frontBack(String str) {
    char c[] = str.toCharArray();

    char temp = c[0];

    c[0] = c[c.length - 1];

    c[c.length - 1] = temp;

    return new String(c);

}

public static void main(String args[]) {

    Str3 s = new Str3();

    String s1 = new String("boy");

    System.out.println(s1);

    String s2 = s.frontBack("boy");

    System.out.println(s2);

}   }